1. Field of the Invention
Embodiments of the invention generally relate to electronic data storage and retrieval systems having magnetic heads capable of reading recorded information stored on magnetic media.
2. Description of the Related Art
In an electronic data storage and retrieval system, a magnetic head typically includes a reader portion having a magnetoresistive (MR) sensor for retrieving magnetically-encoded information stored on a magnetic recording medium or disk. The MR sensor includes multiple layers and operates based on a change of electrical resistivity of certain materials of the MR sensor in the presence of a magnetic field. During a read operation, a bias current is passed through the MR sensor. Magnetic flux emanating from a surface of the recording medium causes rotation of a magnetzation vector of a sensing or free layer of the MR sensor, which in turn causes the change in electrical resistivity of the MR sensor. Since a voltage across the MR sensor is equal to the bias current that is supplied times the resistivity, the change in electrical resistivity of the MR sensor can be detected by measuring the voltage across the MR sensor to provide voltage information that external circuitry can then convert and manipulate as necessary.
A hard magnetic bias structure can be used to suppress magnetic domain wall movement of the free layer to provide a noise-free response from the MR sensor. In construction of the MR sensor, depositing hard bias layers on both sides of the layers forming the MR sensor accomplishes this suppression. In order to promote a desired texture of the hard bias layers, seedlayer structures can be deposited prior to the hard bias layers. The seedlayer structures can affect properties of the hard bias layers including, for example, coercivity and squareness.
Sufficient coercivity prevents disruption of a magnetic configuration of the hard bias layers due to external magnetic fields, such as from the magnetic recording medium. Additionally, the in-plane remnant magnetization (Mr) should be large enough to provide a longitudinal bias flux. If the Mr of the hard bias layers is insufficient, longitudinal bias for the free layer falls short of supplying the necessary flux to ensure noise-free operation of the read head. This implies that the squareness (Mr/saturation magnetization (Ms)) of the hard bias layer along the in-plane direction should be high.
The ability of the seedlayer structure to provide the coercivity and squareness of the hard bias layers can depend on the surface onto which the seedlayer structure is deposited. The seedlayer structure can be deposited onto, for example, crystalline metals such as a platinum manganese (PtMn) layer of the MR sensor. Accordingly, selection of the seedlayer structure requires that the properties of the hard bias layers are not degraded when the seedlayer structure is deposited on the layers of the MR sensor exposed during the partial milling.
Therefore, there exists a need for seedlayer configurations that provide improved properties of hard bias layers of a magnetoresistance sensor.